Process for production of polyamide composite material

ABSTRACT

In the process of the present invention, a polyamide A1 and an organized clay B are mixed mainly by dispersive mixing, and after added with a polyamide A2, mixed mainly by distributive mixing in a corotating intermeshing twin-screw extruder so designed as to effect the dispersive mixing and the distributive mixing. The organized clay B is completely and finely dispersed and distributed throughout the resultant polyamide composite material. Shaped articles such as films and sheets made of the polyamide composite material exhibit excellent gas barrier properties and transparency with little malodor mainly attributable to the decomposed products of the organizing agent for preparing the organized clay B.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a polyamide composite materialcontaining an organized clay, and a production method thereof, and moreparticularly to a polyamide composite material comprising a specificorganized clay and polyamide, which is excellent in gas barrierproperties and transparency, and a production method of the polyamidecomposite material.

[0003] 2. Description of the Prior Art

[0004] Polyamides have been widely used not only as injection-moldingmaterials for automotive, electric and electronic parts, but also aspackaging materials for foodstuffs, beverages, drugs and electronicparts, because of their excellent mechanical properties andprocessability as well as relatively high gas barrier properties. Amongthe polyamides, poly(m-xylylene adipamide) produced by thepolycondensation of a diamine component mainly composed ofm-xylylenediamine and a dicarboxylic acid component mainly composed ofadipic acid (hereinafter occasionally referred to merely as “nylonMXD6”) exhibits a low permeability against gaseous substances such asoxygen and carbon dioxide as compared to other polyamides, andtherefore, has now come into use as packaging materials requiring gasbarrier properties such as films and bottles. In recent years, there isa strong demand for packaging materials capable of keeping freshness offoodstuffs, beverages, etc., for a prolonged period of time. Therefore,the nylon MXD6 has been required to have further enhanced gas barrierproperties.

[0005] One of the methods for enhancing the gas barrier properties ofpolyamides is to uniformly disperse phyllosilicate in a polyamidethereby to prepare a polyamide composite material (for example, JapanesePatent Application Laid-Open No. 62-74957). Japanese Patent ApplicationLaid-Open No. 9-217012 discloses a method of producing a polyamidecomposite material comprising a polyamide having phyllosilicateuniformly dispersed therein by melt-kneading the polyamide and thephyllosilicate in a twin-screw extruder. The proposed methods requiresto apply a strong shear force to a mixture of the nylon MXD6 and theorganized clay by the rotation of a screw in the melt-kneading process.The heat generated by the shearing decomposes the organizing agent inthe organized clay to allow the agglomeration of the clay. Therefore,the clay fails to be completely and finely dispersed and/or distributedin the polyamide to result in the failure in improving the gas barrierproperties. In addition, there occur problems such as deterioration intransparency, increase in YI and malodor development due todecomposition of the organizing agent.

SUMMARY OF THE INVENTION

[0006] An object of the present invention is to solve the above problemsand provide a polyamide composite material containing clay welldispersed and distributed therein, which is excellent in the gas barrierproperties and transparency, and less malodorous.

[0007] As the result of extensive studies in view of solving the aboveproblems, the present inventors have found that a polyamide compositematerial that is produced by melt-kneading a specific polyamide with aspecific organized clay under specific conditions is not only excellentin the gas barrier properties and transparency, but also free frommalodor, this having been not attained in the conventional technique.The present invention has been accomplished on the basis of thisfinding.

[0008] Thus, the present invention provides a process for producing apolyamide composite material comprising a polyamide A1, a polyamide A2,each being produced by polycondensing a diamine component containing 70mol % or higher of m-xylylenediamine with a dicarboxylic acid componentcontaining 50 mol % or higher of a C₄ to C₂₀ α,ω-linear aliphaticdicarboxylic acid, and an organized clay B, by using a corotatingintermeshing twin-screw extruder in which at least a feed section (a)with a feed port (a), a kneading section (a) having a high dispersivemixing capability, a feed section (b) with a feed port (b) and akneading section (b) having a high distributive mixing capability arearranged in this order, the process comprising:

[0009] a step of feeding the polyamide A1 containing a phosphoruscompound in an amount of 500 ppm or smaller in terms of phosphorus atomand having a relative viscosity of 1.1 to 4.7 and the organized clay Binto the feed section (a) through the feed port (a);

[0010] a step of melt-kneading the polyamide A1 and the organized clay Bsubstantially by dispersive mixing in the kneading section (a) to obtaina melt-knead product;

[0011] a step of transporting the melt-knead product from the kneadingsection (a) to the feed section (b), simultaneously feeding thepolyamide A2 having a relative viscosity of 2.0 to 4.7 into the feedsection (b) through the feed port (b); and

[0012] a step of melt-kneading the melt-knead product and the polyamideA2 each from the feed section (b) substantially by distributive mixingin the kneading section (b) to prepare the polyamide composite material.

[0013] The present invention also provides a polyamide compositematerial produced by the above production method, and a packagingmaterial and a packaging container made of the polyamide compositematerial.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a schematic view showing an example of a construction ofa corotating intermeshing twin-screw extruder;

[0015]FIG. 2 is a schematic view showing an example of a construction ofa screw for a corotating intermeshing twin-screw extruder;

[0016]FIG. 3 is a schematic view showing an example of an element havinga high dispersive mixing capability (kneading disk);

[0017]FIG. 4 is a schematic view showing another example of an elementhaving a high dispersive mixing capability (rotor);

[0018]FIG. 5 is a schematic view showing an example of an element havinga high distributive mixing capability (ZME mixing element);

[0019]FIG. 6 is a schematic view showing another example of an elementhaving a high distributive mixing capability (TME mixing element); and

[0020]FIG. 7 is a schematic view showing still another example of anelement having a high distributive mixing capability (screw mixingelement).

DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described in detail below.

[0022] The polyamides A1 and A2 used in the present invention areproduced by polycondensing a diamine component mainly composed ofm-xylylenediamine and a dicarboxylic acid component mainly composed of aC₄ to C₂₀ α,ω-linear aliphatic dicarboxylic acid.

[0023] The diamine component used in the present invention containsm-xylylenediamine in an amount of 70 mol % or higher, preferably 75 mol% or higher and more preferably 80 mol % or higher. If less than 70 mol%, the polyamides A1 and A2 are deteriorated in their gas barrierproperties. Examples of the other diamines for the diamine componentinclude, but are not limited to, aliphatic diamines such astetramethylenediamine, pentamethylenediamine, 2-methylpentanediamine,hexamethylenediamine, heptamethylenediamine, octamethylenediamine,nonamethylenediamine, decamethylenediamine, dodecamethylenediamine,2,2,4-tirmethylhexamethylenediamine and2,4,4-tirmethylhexamethylenediamine; alicyclic diamines such as1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane,1,3-diaminocyclohexane, 1,4-diaminocyclohexane,bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane,bis(aminomethyl)decalin and bis(aminomethyl)tricyclodecane; and aromaticring-containing diamines such as bis(4-aminophenyl)ether,p-phenylenediamine, p-xylylenediamine and bis(aminomethyl)naphthalene.

[0024] The dicarboxylic acid component used in the present inventioncontains a C₄ to C₂₀ α,ω-linear aliphatic dicarboxylic acid in an amountof 50 mol % or higher, preferably 60 mol % or higher and more preferably70 mol % or higher. If less than 50 mol %, the polyamides A1 and A2 aredeteriorated in crystallinity, resulting in poor gas barrier properties.Examples of the C₄ to C₂₀ α,ω-linear aliphatic dicarboxylic acid includealiphatic dicarboxylic acids such as succinic acid, glutaric acid,pimelic acid, suberic acid, azelaic acid, adipic acid, sebacic acid,undecanedioic acid and dodecandioic acid, with adipic acid beingpreferred. Examples of the other dicarboxylic acids usable for thedicarboxylic acid component include aromatic dicarboxylic acids such asterephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylicacid. In addition, a small amount of a molecular weight modifier such asmonoamines and monocarboxylic acids may be added in the polycondensationfor producing the polyamides A1 and A2.

[0025] The polyamides A1 and A2 may be produced by a meltpolycondensation method. For example, the polyamides A1 and A2 may beproduced by heating a nylon salt of m-xylylenediamine and adipic acidunder pressure in the presence of water, and polymerizing the nylon saltin molten state while removing the water added and the water eliminatedby the polycondensation. Alternatively, the polyamides A1 and A2 may beproduced by directly adding m-xylylenediamine to molten adipic acid toallow the polycondensation to proceed under atmospheric pressure. Inthis method, m-xylylenediamine is continuously added to the moltenadipic acid to keep the reaction system in a uniform liquid state whileproceeding the polycondensation by heating the reaction system toprevent the reaction temperature from lowering under the melting pointsof the oligoamides and polyamides being produced.

[0026] The polyamides A1 and A2 produced by the melt-polymerization maybe further polycondensed by a solid-phase polymerization method. Themethod for producing the polyamides A1 and A2 is not limited toparticular ones, and the polyamides A1 and A2 may be produced by anysuitable known methods under known polymerization conditions.

[0027] The relative viscosity of the polyamide A1 is preferably 1.1 to4.7, more preferably 1.5 to 4.4 and still more preferably 1.7 to 4.2. Ifless than 1.1, the organized clay B becomes difficult to be subject to ashear force during the melt-kneading of the polyamide A1 with theorganized clay B because of the excessively low melt viscosity, therebyfailing to attain a uniform dispersion and/or distribution of theorganic clay B. If more than 4.7, an excessive torque tends to beapplied to the extruder thereby to make the production of the polyamidecomposite material difficult.

[0028] The relative viscosity referred to herein may be measured by aCanon Fenske viscometer, etc. on a solution prepared by dissolving 1 gof polyamide A1 or A2 in 100 ml of a 96% sulfuric acid at 25° C. Thepolyamide A1 used in the present invention has a number-averagemolecular weight of about 2,000 to 50,000.

[0029] The relative viscosity of the polyamide A2 is preferably 2.0 to4.7, more preferably 2.05 to 4.4 and still more preferably 2.1 to 4.2.If less than 2.0, the viscosity of the resultant polyamide compositematerial becomes too low. If more than 4.7, an excessive torque tends tobe applied to an extruder thereby to make the production of thepolyamide composite material difficult. The polyamide A2 has anumber-average molecular weight of about 14,000 to 50,000.

[0030] The polyamides A1 and A2 may contain a phosphorus compound toenhance a processing stability during the melt molding and prevent thediscoloration of the polyamides A1 and A2. An alkali metal- or alkalineearth metal-containing phosphorus compound is preferably used as thephosphorus compound. Examples thereof include phosphates, hypophosphitesand phosphites of alkali metal or alkaline earth metal such as sodium,magnesium and calcium, with the alkali metal or alkaline earth metalhypophosphite being preferred because of its extremely excellent effectof preventing the discoloration of the polyamides A1 and A2. Theconcentration of the phosphorus compound in the polyamides A1 and A2 ispreferably 1 to 500 ppm, more preferably 350 ppm or lower and still morepreferably 200 ppm or lower in terms of phosphorus atom. If exceeding500 ppm, no additional effect of preventing the discoloration isobtained, instead, the haze of films produced from the polyamidecomposite material is increased.

[0031] The polyamide A1 is subject to a strong shear stress in thekneading section (a). Therefore, if the phosphorus compound is notadded, the polyamide A1 tends to be thermally degraded to increase YI,thereby reducing the commercial value of the polyamide compositematerial.

[0032] The organized clay B used in the present invention is prepared bysubjecting clay to a swelling treatment with an organizing agent.Examples of the clays for preparing the organized clay B include mica,vermiculite and smectite, and preferably a dioctahedral phyllosilicatesuch as montmorillonite, beidellite and nontronite and a trioctahedralphyllosilicate such as hectorite and saponite, each having a chargedensity of 0.25 to 0.6. Of these clays, particularly preferred ismontmorillonite because of its high swelling property that allows theswelling of montmorillonite by the penetration of the organizing agentto easily expand the interlaminar space, thereby making montmorilloniteeasily dispersible and distributable in the polyamide compositematerial.

[0033] As the organizing agent, preferred are quaternary ammonium salts,and more preferred are quaternary ammonium salts having at least onealkyl group with 12 or more carbon atoms. Examples of the organizingagents include trimethylalkylammonium salts such astrimethyldodecylammonium salt, trimethyltetradecylammonium salt,trimethylhexadecylammonium salt, trimethyloctadecylammonium salt andtrimethyleicosylammonium salt; trimethylalkenylammonium salts such astrimethyloctadecenylammonium salt and trimethyloctadecadienylammoniumsalt; triethylalkylammonium salts such as triethyldodecylammonium salt,triethyltetradecylammonium salt, triethylhexadecylammonium salt andtriethyloctadecylammonium salt; tributylalkylammonium salts such astributyldodecylammonium salt, tributyltetradecylammonium salt,tributylhexadecylammonium salt and tributyloctadecylammonium salt;dimethyldialkylammonium salts such as dimethyldidodecylammonium salt,dimethylditetradecylammonium salt, dimethyldihexadecylammonium salt,dimethyldioctadecylammonium salt and dimethylditallowammonium salt;dimethyldialkenylammonium salts such as dimethyldioctadecenylammoniumsalt and imethyldioctadecadienylammonium salt; diethyldialkylammoniumsalts such as diethyldidodecylammonium salt, diethylditetradecylammoniumsalt, diethyldihexadecylammonium salt and diethyldioctadecylammoniumsalt; dibutyldialkylammonium salts such as dibutyldidodecylammoniumsalt, dibutylditetradecylammonium salt, dibutyldihexadecylammonium saltand dibutyldioctadecylammonium salt; methylbenzyldialkylammonium saltssuch as methylbenzyldihexadecylammonium salt; dibenzyldialkylammoniumsalts such as dibenzyldihexadecylammonium salt; trialkylmethylammoniumsalts such as tridodecylmethylammonium salt, tritetradecylmethylammoniumsalt ant trioctadecylmethylammonium salt; trialkylethylammonium saltssuch as tridodecylethylammonium salt; trialkylbutylammonium salts suchas tridodecylbutylammonium salt; methyldihydroxyethyl hydrogenatedtallowammonium salts; and ω-amino acids such as 4-amino-n-butyric acid,6-amino-n-caproic acid, 8-aminocaprylic acid, 10-aminodecanoic acid,12-aminododecanoic acid, 14-aminotetradecanoic acid,16-aminohexadecanoic acid and 18-aminooctadecanoic acid. Of theseorganizing agents, preferred are trimethyldodecylammonium salts,trimethyltetradecylammonium salts, trimethylhexadecylammonium salts,trimethyloctadecylammonium salts, dimethyldidodecylammonium salts,dimethylditetradecylammonium salts, dimethyldihexadecylammonium salts,dimethyldioctadecylammonium salts and dimethylditallowammonium salts.These organizing agents may be used singly or in combination of two ormore. In addition, quaternary ammonium salts having a glycol group suchas polyethylene glycol and propylene glycol may be used as theorganizing agent.

[0034] The content of the organizing agent is preferably 10 to 60% byweight of the organized clay B. If less than 10% by weight, the claybecomes difficult to be dispersed and/or distributed. If more than 60%by weight, the organizing agent tends to be degraded or decomposed byheat to cause the clay to agglomerate, thereby failing to attain acomplete fine dispersion and/or distribution of the clay, and developingmalodor attributable to decomposed products of the organizing agent suchas amines and ammonia.

[0035] The initiation temperature of mass change as defined in JISK-7120 of the organized clay B is preferably 210° C. or higher, morepreferably 220° C. or higher and still more preferably 230° C. or higherwhen measured by thermogravimetry under nitrogen flow. If lower than210° C., the organizing agent tends to be degraded or decomposed by heatin the melt-kneading to cause the clay to agglomerate, thereby failingto attain a complete and fine dispersion and/or distribution of the clayand developing malodor attributable to decomposed products of theorganizing agent such as amines and ammonia.

[0036] In the present invention, the uniform dispersion and distributionof the organized clay B may be confirmed by a method of observing theclay in a sample under a transmission electron microscope, a method ofobserving the surface of sample under a scanning electron microscope, amethod of measuring the interlaminar distance of the clay by an X-raydiffraction method, etc. The methods using the electron microscopesenables direct measurement of the interlaminar distance of the clay. Inthe X-ray diffraction method, when no peak attributable to the clay isobserved in the diffraction profile, the dispersion and distribution ofthe clay is considered good.

[0037] The polyamide composite material of the present invention isproduced by melt-kneading the polyamide A1, the polyamide A2 and theorganized clay B in a corotating intermeshing twin-screw extruder.

[0038] The corotating intermeshing twin-screw extruder usable in thepresent invention is designed such that at least a feed section (a) witha feed port (a), a kneading section (a) having a high dispersive mixingcapability, a feed section (b) with a feed port (b), and a kneadingsection (b) having a high distributive mixing capability are arranged inthis order, and may further include a transport section for transportingthe feedstocks and the melt-knead products towards the downstream end ofthe extruder (FIG. 1).

[0039] In general, the corotating intermeshing twin-screw extruder is aself-cleaning extruder in which two screws are rotated in the samedirections at an intermesh ratio of 1.2 to 1.7. The intermesh ratio iscalculated by dividing an outer screw diameter by a short screwdiameter. The extruder may be provided with a vent opened to atmospherefor discharging air contained in the feedstocks to improve the feedingability. The kneading sections may not necessarily be self-cleaning. Thescrew may be a single flight screw, a double flight screw or a tripleflight screw, with the double flight screw being most common.

[0040] The corotating intermeshing twin-screw extruder is most effectiveto produce the polyamide composite material because a shear stresssufficient for dispersing and distributing the clay is obtained, but asingle-screw extruder will be undesirable because a shear stresssufficient for dispersing and distributing the clay is not obtained.Although the polyamide composite material may be also produced using acounterrotating twin-screw extruder, a non-intermeshing twin-screwextruder, etc., these extruders are less effective for general-purposeuse and may fail to produce a shear force sufficient for uniformlydispersing and distributing the clay.

[0041] In the process of the present invention, the polyamide A1 and theorganized clay B are fed through the feed port (a) and melt-kneaded inthe kneading section (a) having a high dispersive mixing capability.Then, at any suitable timing subsequent to the above melt-kneading, thepolyamide A2 is fed through the feed port (b) provided at the midportion of a cylinder of the twin-screw extruder, and melt-kneaded withthe melt-knead product from the kneading section (a) in the kneadingsection (b) having a high distributive mixing capability to produce thepolyamide composite material of the present invention. If a whole amountof the polyamide A1, the polyamide A2 and the organized clay B are fedthrough the feed port (a), the polyamides A1 and A2 come to beexcessively hot by a shear force applied thereto to lower the viscosity,resulting in poor dispersion and/or distribution of the organized clayB. In addition, since the polyamides A1 and A2 are degraded or damagedby the heat generated during the kneading, YI is increased, the amountof gels or fish eyes is increased and the draw-down is likely to occurin the process for forming films and sheets because of the loweredmolecular weight and melt viscosity, thereby reducing the commercialvalues of the resultant composite material and its shaped articles. Ifthe dispersive mixing capability of the kneading section (a) is low, theorganized clay is not sufficiently crushed nor finely dispersed owing toan insufficient shear stress applied thereto. If the distributive mixingcapability of the kneading section (b) is low, the melt-knead product ofthe polyamide A1 and the organized clay B tends to be insufficientlymixed with the polyamide A2 supplied through the feed port (b).

[0042] The feed port is a part through which resins, etc., are suppliedinto the extruder. A belt feeder, a screw feeder, a vibration feeder,etc. may be used to feed the polyamides A1 and A2 and the organized clayB, although not limited thereto. The polyamide A1 and the organized clayB may be separately fed by respective feeders, or may be fed after beingdry-blended.

[0043] The feed section has a function for transporting the feedstocksfed through the feed ports to the next kneading section, and is providedwith a screw therefor.

[0044] The polyamide A2 may be supplied through the feed port (b) by aside-feeding method using extruder, etc., although not limited thereto.To improve and stabilize the side-feeding performance, the extruder maybe provided with a vent opened to atmosphere.

[0045] The kneading section is a portion in which the feedstocks aresubjected to shearing, distribution, diffusion, extensive flow, etc., bythe screws or barrels to uniformly disperse or distribute the organizedclay B in the polyamide A1 or A2 or the polyamides A1 and A2. The“kneading” used herein means to subject the feedstocks to shearing,distribution, diffusion, extensive flow, etc., by the screws or barrelsto uniformly disperse or distribute the organized clay B in thepolyamide A1 or A2 or the polyamides A1 and A2.

[0046] As illustrated in FIG. 2, the screws of the twin-screw extruderused in the present invention preferably comprise portions correspondingto the respective sections of the extruder. Specifically, to finelydisperse or distribute the organic clay B in the polyamide, the screwpreferably comprises a feed screw portion for transporting thefeedstocks (polyamide A1 and organized clay B) from the feed port (a)towards the downstream end of the extruder (corresponding to the feedsection (a)); a portion having a group of elements with a highdispersive mixing capability for melt-kneading the feedstocks from thefeed section (a) (corresponding to the kneading section (a)); a feedscrew portion for transporting the kneaded feedstocks from the kneadingsection (a) together with the polyamide A2 fed through the feed port (b)(corresponding to the feed section (b)); a portion having a group ofelements with a high distributive mixing capability for melt-kneadingthe kneaded feedstocks from the kneading section (a) and the polyamideA2 fed through the feed port (b) (corresponding to the kneading section(b)); and a feed screw portion for transporting the kneaded feedstocksfrom the kneading section (b) towards the downstream end of the extruder(corresponding to the transport section). An extruder that is notprovided with the kneading section (a) and/or (b) fails to exert theactions of shearing, distribution, diffusion, etc. on the feedstockssufficient for uniformly and finely dispersing or distributing theorganic clay B throughout the polyamides A1 and A2.

[0047] The mixing action of materials is generally classified intodispersive mixing and distributive mixing. The dispersive mixing is amixing action accompanied by the reduction in particle size, namely, thecrush of particles. The distributive mixing is a mixing action by theposition exchange of a particle with another. Similarly, in the presentinvention, the mixing with high dispersive mixing capability means amixing substantially governed by the crush of the polyamide A1 and theparticles of the organized clay B, and the mixing with high distributivemixing capability means a mixing substantially governed by the positionexchange of the polyamides A1 and A2 with particles of the organizedclay B. It should not be construed that the dispersive mixing is notaccompanied by the distributive mixing, and vice versa. Examples of theelements having a high dispersive mixing capability include, as shown inFIGS. 3 and 4, a rotor and a kneading disk which has a broad disk width,for example, has a W/D ratio of 0.15 to 1.5, wherein W is a disk widthand D is a screw diameter, although not limited thereto. Examples of theelements having a high distributive mixing capability include, as shownin FIGS. 5 to 7, a rotor, a notched full-flight disk, a mixing gear anda kneading disk which has a narrow disk width, for example, has a W/Dratio of 0.02 to less than 0.15, although not limited thereto. Thenotched full-flight disk may be reversely flighted. The mixing gear mayor may not be self-cleaning. The helix angle of the kneading disk is notparticularly restricted, and kneading disks having different helixangles may be combinedly used. The maximum shear stress produced by therotor is smaller than that of the kneading disk, but the rotor applies auniform shear stress to the feedstocks. Therefore, the rotor isconsidered to have both the dispersive mixing capability and thedistributive mixing capability. These elements may be appropriatelycombined with each other to constitute screws corresponding to thekneading sections (a) and (b).

[0048] The portion of the screw corresponding to the kneading section(a) is preferably a high dispersive-mixing screw comprising at least oneelement, such as a reverse full-flight disk and a sealing disk, having apressure-dropping function to allow the kneading section (a) to besufficiently filled with the feedstocks, and at least one elementselected from a kneading disk having a broad disk width and a rotor. Ifthe portion of the screw corresponding to the kneading section (a) ishighly distributive-mixing, the shear force applied to the feedstocks isinsufficient to result in a poor dispersion of the organized clay B. Ifthe elements such as a reverse full-flight disk and a sealing disk arenot used in the kneading section (a), the feedstocks fail tosufficiently fill the kneading section (a) and a sufficient shearingresidence time is not attained, resulting in a poor dispersion of theorganized clay B.

[0049] The portion of the screw corresponding to the kneading section(a) preferably comprises, at least partly, a kneading disk having aratio W/D of preferably 0.15 to 1.5, more preferably 0.2 or higher andstill more preferably 0.3 or higher, wherein W is the width of thekneading disk and D is the screw diameter of the twin-screw extruder. Ifless than 0.15, the distributive mixing capability is too strong. Whenthe ratio W/D is 0.15 or higher, the dispersive mixing capabilitybecomes strong, resulting in a good dispersion of the organized clay B.

[0050] The portion of the screw corresponding to the kneading section(b) is preferably a high distributive-mixing screw comprising at leastone element, such as a reverse full-flight disk and a sealing disk,having a pressure-dropping function to allow the kneading section (b) tobe sufficiently filled with the feedstocks, and at least one elementselected from a kneading disk having a narrow disk width, a rotor, anotched flight disk and a mixing gear. If the portion of the screwcorresponding to the kneading section (b) is highly dispersive-mixing,an excessive shearing force is applied to the polyamides A1 and A2 tocause an excessive heat generation of the polyamide A1 and A2, therebydegrading and damaging the polyamides A1 and A2 to increase YI, increasethe amount of gels and fish eyes and cause the drawdown in the processfor forming films and sheets because of the lowered molecular weight andmelt viscosity, this reducing the commercial values of the resultantcomposite material and its shaped articles. If the elements such as areverse full-flight disk and a sealing disk are not used in the kneadingsection (b), the filling thereof with the feedstocks is lowered and asufficient shearing residence time is not attained, resulting in a poordistribution of the organized clay B.

[0051] The length of each portion of the screw corresponding to thekneading sections (a) and (b) is preferably 10 to 60% and morepreferably 20 to 55% of the overall length of the screw. If less than10%, the shear force applied to the feedstocks is insufficient to resultin a poor dispersion and/or distribution of the organized clay B. Ifmore than 60%, the polyamides A1 and A2 are subject to increased heathistory to be degraded, thereby causing the discoloration and theincrease in the amount of gels and fish eyes. Further, the organizingagent in the organized clay B is degraded or decomposed by heat to causethe clay to agglomerate, thereby failing to attain a complete and finedispersion and/or distribution of the clay and developing malodorattributable to the decomposed products of the organizing agent such asamines and ammonia. The portion of the screw corresponding to thekneading section (a) or (b) may be divided into two or more parts, aslong as the length of the portion is within 10 to 60% of the overalllength of the screw.

[0052] The melt kneading temperature in the kneading sections (a) and(b) is equal to or higher than the melting points of the polyamides A1,A2, and simultaneously, equal to or lower than the temperature where theorganized clay B loses its weight by 10%, preferably by 8%, and morepreferably by 5% when measure by thermogravimetry. If the melt kneadingtemperature is within the above range, the uniform fine dispersion andthe uniform fine distribution of the organized clay B can be easilyattained. The thermogravimetry is carried out according to the measuringmethod of JIS K-7120, for example, under nitrogen flow at a temperaturerise rate of 10° C./min using a simultaneousthermogravimetric/differential thermal analyzer “DTG-50” available fromShimadzu Corporation. The actual resin temperature during the kneadingtends to be higher than the temperature of the extruder because of theshearing heat generated by the rotation of screws. Therefore, it isrecommended to measure the resin temperature as accurately as possible,for example, by measuring the resin temperature at the downstream end ofthe extruder. If exceeding the temperature where the organized clay Bloses its weight by 10%, a large part of the organizing agent in theorganized clay B is thermally degraded or decomposed to allow the clayto agglomerate, thereby failing to attain a complete fine dispersion anddistribution of the clay, and developing malodor attributable todecomposed products of the organizing agent such as amines and ammonia.If less than the melting points of the polyamides A1, A2, the organizedclay B is not finely dispersed and finely distributed because thepolyamide is not melted.

[0053] In the melt kneading of the polyamide A1, A2 and the organizedclay B for the production of the polyamide composite material of thepresent invention, the specific energy provided by the extruder to thefeedstocks therein is preferably 0.2 to 0.45 kWh/kg on average betweenthe feed port (a) and the downward end of the extruder. The specificenergy referred to herein means the energy provided to a unit weight offeedstocks per unit time. If less than 0.2 kWh/kg, the energy isinsufficient for kneading to fail to attain the fine dispersion and thefine distribution of the organized clay B. If larger than 0.45 kWh/kg,the polyamide A1, A2 receive an excessive energy to lower the viscosityof the polyamide, thereby likely to cause insufficient fine dispersionand fine distribution of the organized clay B. In addition, thepolyamide is degraded and damaged. As a result, YI is increased, theamount of gels or fish eyes is increased and the draw-down is likely tooccur in the process for forming films and sheets because of the loweredmolecular weight and melt viscosity, thereby reducing the commercialvalues of the resultant composite material and its shaped articles.

[0054] The overall residence time for melt-kneading the polyamide A1, A2and the organized clay B in the twin-screw extruder is preferably 60 to1200 s, more preferably 80 to 1000 s, and still more preferably 100 to800 s. The overall residence time referred to herein means the timerequired for kneading, and more specifically the time taken from thefeed of the polyamide A1 and the organized clay B through the feedportion (a) until the feedstocks are extruded from the die. The overallresidence time may be determined, for example, by measuring the timefrom feeding a colored pellet, etc. through the feed portion (a) untilthe color of the strand being extruded from the die is changed. Ifshorter than 60 s, insufficient fine dispersion and fine distribution ofthe organized clay B are likely to be caused. If longer than 1200 s, thepolyamides A1 and A2 are subject to increased heat history to bedegraded, thereby causing the discoloration and the increase in theamount of gels and fish eyes. Further, the organizing agent in theorganized clay B is degraded or decomposed by heat to cause the clay toagglomerate, thereby failing to attain a complete and fine dispersionand distribution of the clay and developing malodor attributable to thedecomposed products of the organizing agent such as amines and ammonia.

[0055] The residence time of the polyamide A2 from being fed through thefeed port (b) until being extruded from the die of the extruder ispreferably 10 to 600 s, more preferably 15 to 400 s, and still morepreferably 20 to 300 s.

[0056] In the present invention, the polyamide A1, the polyamide A2 andthe organized clay B are preferably fed into the twin-screw extruder andmelt-kneaded therein so as to satisfy the following conditions (1) and(2):

[0057] (1) X/Y is preferably 1 to 8, more preferably 1.5 to 6 and stillmore preferably 2 to 4, and

[0058] (2) 100Y/(X+Y+Z) is preferably 1 to 20, more preferably 1.2 to 18and still more preferably 1.5 to 16,

[0059] wherein X is the weight (kg) of the polyamide A1 fed through thefeed port (a), Y is the weight (kg) of the organized clay B fed throughthe feed port (a), and Z is the weight (kg) of the polyamide A2 fedthrough the feed port (b).

[0060] If X/Y exceeds 8, the amount of the polyamide A1 to be degradedand damaged by the heat generation increases to increase YI, increasethe amount of gels and fish eyes and cause the drawdown in the processfor forming films and sheets because of the lowered molecular weight andmelt viscosity, thereby reducing the commercial values of the resultantcomposite material and its shaped articles. When X/Y is less than 1, theamount of the organizing agent to be degraded and damaged by heatincreases to cause the agglomeration of the organized clay B, therebyfailing to attain a complete and fine dispersion and/or distribution ofthe clay in the polyamide composite material and also developing malodorattributable to the decomposed products of the organizing agent such asamines and ammonia

[0061] If 100Y/(X+Y+Z) is less than 1, the effect of improving the gasbarrier properties is insufficient. If exceeding 10, it becomesdifficult to uniformly disperse or distribute the organized clay Bthroughout the polyamides A1 and A2.

[0062] The number-average molecular weight of the overall polyamide(polyamide A1+polyamide A2) is 10,000 to 50,000. The number-averagemolecular weight may be appropriately selected according to applicationsof the polyamide composite material and molding methods. For example,when the polyamide composite material is required to have a fluidity ofcertain degree in the film-forming process, the number-average molecularweight is about 20,000 to 30,000, and when the polyamide compositematerial is required to have a melt strength in the sheet-formingprocess, the number-average molecular weight is about 30,000 to 45,000,although not limited thereto.

[0063] The polyamide composite material of the present invention has awater content of less than 0.2% by weight in view of a good moldability.If the water content is 2% by weight or higher, the reduction ofmolecular weight, the formation of gelled mass and bubbles and thedrawdown are likely to occur. Therefore, the polyamide compositematerial is preferably dried before use to reduce the water content. Thedrying of the polyamide composite material may be conducted by knownmethods, for example, a method of removing water from the polyamidecomposite material by evacuating the interior of a cylinder by a vacuumpump during the melt extrusion of the polyamide composite material froma vented extruder; and a method of drying the polyamide compositematerial by heating in a tumbler (rotary vacuum vessel) at a temperaturenot higher than the melting points of the polyamide A1 and A2 underreduced pressure, although not limited thereto.

[0064] The polyamide composite material of the present invention maycontain another resin such as nylon 6, nylon 66, nylon 6,66, polyestersand polyolefins unless the effects of the present invention areadversely affected. The polyamide composite material may further containvarious additives, for example, inorganic fillers such as glass fibersand carbon fibers; plate-like inorganic fillers such as glass flakes,talc, kaolin and mica; impact modifiers such as various elastomers;nucleating agents; lubricants such as fatty acid amides and fatty acidmetal salts; antioxidants such as copper compounds, organic or inorganichalogen compounds, hindered phenols, hindered amines, hydrazinecompounds, sulfur compounds and phosphorus compounds; heat stabilizers;discoloration inhibitors; ultraviolet light absorbers such asbenzotriazole compounds; mold release agents; plasticizers; colorants;flame retardants; oxygen-capturing agents such as cobalt-containingcompounds; and inhibitors such as alkali compounds for preventing thegelation of the polyamides A1 and A2.

[0065] The polyamide composite material of the present invention isexcellent in gas barrier properties and transparency, and shows a stablemelting properties. The polyamide composite material may be formed intosingle-layer films or sheets using, for example, T-die extruders orblown film extruders, and further may be formed into packaging materialssuch as multi-layer films and sheets by laminating a layer made ofpolyethylene, polypropylene, nylon 6, PET, metal foil, paper, etc., byan extrusion laminating method or a co-extrusion method. In addition,the polyamide composite material may be applied to wrapping materialsand packaging containers having various shapes such as pouches, lids,bottles, cups, trays and tubes. The packaging containers made of thepolyamide composite material of the present invention exhibit excellentgas barrier properties and transparency and are useful to preservevarious products. Examples of the products to be preserved includeliquid beverages such as carbonated beverage, juice, water, milk, sake,whisky, shochu, coffee, tea, jelly beverage and healthy beverage;seasonings such as liquid seasoning, sauce, soy sauce, dressing, liquidsoup stock, mayonnaise, miso and grated spices; pasty foodstuffs such asjam, cream and chocolate paste; liquid foodstuffs represented by liquidprocessed foodstuffs such as liquid soup, boiled food, pickles and stew;raw or boiled noodles such as buckwheat noodle, wheat noodle and Chinesenoodle; uncooked or boiled rice such as polished rice, water-conditionedrice and washing-free rice; processed rice products such as boiled ricemixed with fish and vegetables, rice boiled together with red beans andrice gruel; high water content foodstuffs represented by powderyseasonings such as powdery soup and powdery soup stock; low watercontent foodstuffs such as dehydrated vegetables, coffee beans, coffeepowder, leaf tea and confectioneries made of cereals; solid and liquidchemicals such as agricultural chemicals and insecticides; and liquid orpast products such as drugs, beauty wash, cosmetic cream, milky lotion,hair dressing, hair dye, shampoo, soap and detergent.

[0066] The present invention will be described in more detail below withreference to the following examples. In the following examples, thepolyamide composite materials were evaluated by the following methods.

[0067] (1) Relative Viscosity η_(r)

[0068] One gram of polyamide was accurately weighed and dissolved in 100cc of 96% sulfuric acid at 20 to 30° C. under stirring. After completedissolution, 5 cc of the resulting solution was immediately placed in aCanon Fenske viscometer. After the viscometer was allowed to stand in athermostatic chamber maintained at 25±0.03° C. for 10 min, a droppingtime (t) was measured. Also, a dropping time (t₀) of the 96% sulfuricacid itself was measured. The relative viscosity η_(r) of the polyamidewas calculated from the measured t and t₀ according to the followingformula:

Relative Viscosity η_(r)=(t)/(t ₀).

[0069] (2) Water Content

[0070] Measured at 235° C. for 50 min in a nitrogen atmosphere by usinga trace water analyzer “CA-05” available from Mitsubishi Chemical Corp.

[0071] (3) Haze

[0072] Measured on a film according to ASTM D1003 using a colordifference-turbidity meter “COH-300A” available from Nippon DenshokuKogyo Co., Ltd.

[0073] (4) Oxygen Permeability

[0074] Measured on a film at 23° C. and a relative humidity of 60%according to ASTM D3985 using “OX-TRAN 10/50A” available from ModernControls Co., Ltd.

[0075] (5) X-Ray Diffraction (XRD)

[0076] Performed using an analyzer “MINIFLEX” available from RigakushaCo., Ltd. under conditions of: CuKα X-ray source, 4.2° of scatteringslit, 0.3 mm of light-receiving slit, 30 kV of lamp voltage, 15 mA oflamp current, 2 to 50° of scanning range, 0.02° of sampling width, and5°/min of scanning speed.

[0077] (6) YI

[0078] Measured on pellets by a transmission method according to ASTMD1003 using “Z-Σ80 Color Measuring System” available from NipponDenshoku Kogyo Co., Ltd.

[0079] The organized clay used in the examples and comparative exampleswas “NEW D ORBEN” available from Shiraishi Kogyo Co., Ltd., which wasprepared by organizing montmorillonite with dimethyldioctadecylammoniumsalt.

EXAMPLE 1

[0080] m-Xylylenediamine was polycondensed with adipic acid in a moltenstate for a predetermined period of time and extruded from a nozzle atthe bottom of the polymerization vessel into a form of strand, which wascut into pellets after air cooling to obtain two types ofpoly(m-xylylene adipamide) (PA1 and PA2). PA1 had a relative viscosityη_(r) of 2.56 and a phosphorus atom concentration of 150 ppm, and PA2had a relative viscosity η_(r) of 2.63. Through the feed port (a), PA1was fed using a belt feeder at a rate of 6.12 kg/h, and the organizedclay was fed using a screw feeder at a rate of 2.04 kg/h, whileside-feeding PA2 through the feed port (b) using a vibration feeder at arate of 51.84 kg/h. The feedstocks were melt-kneaded in a ventedcorotating intermeshing twin-screw extruder equipped with the screws asshown in FIG. 2, and dried at 140° C. for 5 h to produce 100 kg of apolyamide composite material (C1). C1 had a relative viscosity η_(r) of2.50 and YI of 44.6, and was free from amine and ammonia odorattributable to the decomposition of the organizing agent. The pelletswere fed to a single-screw extruder having a cylinder diameter of 20 mmat a feed rate of 1.2 kg/h, and extruded through a T-die into a form offilm, which was solidified on a roll to produce a film having athickness of 80 μm. The film was extremely excellent in gas barrierproperties and transparency as was evidenced by having a goodappearance, a haze of 1.3%, and an oxygen permeability of 0.01cc·mm/m²·day·atm. XRD showed no remarkable peak attributable to theclay.

EXAMPLE 2

[0081] m-Xylylenediamine was polycondensed with adipic acid in a moltenstate for a predetermined period of time and extruded from a nozzle atthe bottom of the polymerization vessel into a form of strand, which wascut into pellets after air cooling to obtain two types ofpoly(m-xylylene adipamide) (PA3 and PA4). PA3 had a relative viscosityη_(r) of 2.45 and a phosphorus atom concentration of 150 ppm, and PA4had a relative viscosity η_(r) of 2.68. Through the feed port (a), PA3was fed using a belt feeder at a rate of 6.12 kg/h, and the organizedclay was fed using a screw feeder at a rate of 2.04 kg/h, whileside-feeding PA4 through the feed port (b) using a vibration feeder at arate of 51.84 kg/h. The feedstocks were melt-kneaded in a ventedcorotating intermeshing twin-screw extruder equipped with the screws asshown in FIG. 2, and dried at 140° C. for 5 h to produce 100 kg of apolyamide composite material (C2). C2 had a relative viscosity η_(r) of2.60 and YI of 44.0, and was free from amine and ammonia odorattributable to the decomposition of the organizing agent. The pelletswere fed to a single-screw extruder having a cylinder diameter of 20 mmat a feed rate of 1.2 kg/h, and extruded through a T-die into a form offilm, which was solidified on a roll to produce a film having athickness of 80 μm. The film was extremely excellent in gas barrierproperties and transparency as was evidenced by having a goodappearance, a haze of 2.0%, and an oxygen permeability of 0.02cc·mm/m²·day·atm. XRD showed no remarkable peak attributable to theclay.

[0082] As seen from Examples 1 and 2, in the polyamide compositematerials produced by the method of the present invention, the organizedclay was well dispersed and distributed throughout the polyamides, YIwas low, and the organizing agent and polyamides were little degraded.The polyamide composite materials provided films with high-qualityhaving extremely excellent gas barrier properties and transparency.

[0083] In general, a poor dispersion and distribution of clay results inincreased hazes and insufficient gas barrier properties of moldedarticles because of the presence of agglomerates of clay and voidsaround the agglomerates. In contrast, in the polyamide compositematerials produced by the process of the present invention, thedispersion and distribution of the clay is especially excellent.Therefore, in the films, etc., produced therefrom, the haze is loweredto provide an excellent transparency, and the gas barrier properties areimproved to significantly reduce the oxygen permeability.

[0084] Thus, the polyamide composite material and the production processaccording to the present invention are excellent in the dispersion anddistribution of the organized clay as compared to those conventionallyknown. Therefore, the polyamide composite material is excellent in gasbarrier properties and transparency, and additionally, is subject tolittle degradation of polyamides and generates little malodor, resultingin high commercial value and excellent industrial value as compared toconventional materials.

What is claimed is:
 1. A process for producing a polyamide compositematerial comprising a polyamide A1, a polyamide A2, each being producedby polycondensing a diamine component containing 70 mol % or higher ofm-xylylenediamine with a dicarboxylic acid component containing 50 mol %or higher of a C₄ to C₂₀ α,ω-linear aliphatic dicarboxylic acid, and anorganized clay B, by using a corotating intermeshing twin-screw extruderin which at least a feed section (a) with a feed port (a), a kneadingsection (a) having a high dispersive mixing capability, a feed section(b) with a feed port (b) and a kneading section (b) having a highdistributive mixing capability are arranged in this order, the processcomprising: a step of feeding the polyamide A1 containing a phosphoruscompound in an amount of 500 ppm or smaller in terms of phosphorus atomand having a relative viscosity of 1.1 to 4.7 and the organized clay Binto the feed section (a) through the feed port (a); a step ofmelt-kneading the polyamide A1 and the organized clay B substantially bydispersive mixing in the kneading section (a) to obtain a melt-kneadproduct; a step of transporting the melt-knead product from the kneadingsection (a) to the feed section (b), and simultaneously feeding thepolyamide A2 having a relative viscosity of 2.0 to 4.7 into the feedsection (b) through the feed port (b); and a step of melt-kneading themelt-knead product and the polyamide A2 each from the feed section (b)substantially by distributive mixing in the kneading section (b) toprepare the polyamide composite material.
 2. The process according toclaim 1, comprising: a step of transporting the polyamide A1 and theorganized clay B towards a downstream end of the corotating intermeshingtwin-screw extruder by a transport portion (a) of a screw provided tothe extruder; a step of melt-kneading the polyamide A1 and the clay Beach from the feed section (a) by a portion of the screw comprising agroup of elements having a high dispersive mixing capability to obtainthe melt-knead product (a); a step of transporting the melt-kneadproduct (a) from the kneading section (a) and the polyamide A2 from thefeed port (b) towards the downstream end of the extruder by a transportportion (b) of the screw; a step of melt-kneading the melt-knead product(a) and the polyamide A2 each from the feed section (b) by a portion ofthe screw comprising a group of elements having a high distributivemixing capability to obtain a melt-knead product (b); and a step oftransporting the melt-knead product (b) towards the downstream end ofthe extruder by a transport portion (c) of the screw.
 3. The processaccording to claim 1, wherein the polyamide A1 and the organized clay Bare melt-kneaded in the kneading section (a) by a screw having a highdispersive mixing capability which comprises at least one element havinga pressure-dropping function to allow the kneading section (a) to befilled with the polyamide A1 and the organized clay B, and at least oneelement selected from the group consisting of a kneading disk having abroad disk width and a rotor.
 4. The process according to claim 1,wherein the melt-knead product from the kneading section (a) and thepolyamide A2 fed through the feed port (b) are melt-kneaded in thekneading section (b) by a screw having a high distributive mixingcapability which comprises at least one element having apressure-dropping function to allow the kneading section (b) to befilled with the melt-knead product and the polyamide A2, and at leastone element selected from the group consisting of a kneading disk havinga narrow disk width, a rotor, a notched flight disk and a mixing gear.5. The process according to claim 3, wherein the element having thepressure-dropping function is an reverse full-flight disk and/or asealing disk.
 6. The process according to claim 4, wherein the elementhaving the pressure-dropping function is an reverse full-flight diskand/or a sealing disk.
 7. The process according to claim 3, wherein atleast a part of the kneading section (a) is provided with a kneadingdisk having a ratio W/D of 0.15 or higher wherein W is a width of thekneading disk and D is a screw diameter of the twin-screw extruder. 8.The process according to claim 4, wherein at least a part of thekneading section (a) is provided with a kneading disk having a ratio W/Dof 0.15 or higher wherein W is a width of the kneading disk and D is ascrew diameter of the twin-screw extruder.
 9. The process according toclaim 2, wherein a length of the screw in each of the kneading sections(a) and (b) is 10 to 60% of an overall length of the screw.
 10. Theprocess according to claim 1, wherein a melt-kneading temperature in thekneading sections (a) and (b) is equal to or higher than melting pointsof the polyamides A1 and A2, and simultaneously, equal to or lower thana temperature where the organized clay B loses its weight by 10% whenmeasured by thermogravimetry according to JIS K-7120.
 11. The processaccording to claim 1, wherein a specific energy provided by thecorotating intermeshing twin-screw extruder to the polyamides A1 and A2and the organized clay B is 0.2 to 0.45 kWh/kg on average between thefeed port (a) and the downward end of the extruder.
 12. The processaccording to claim 1, wherein the kneading is performed so that anoverall residence time in the corotating intermeshing twin-screwextruder is 60 to 1200 s.
 13. The process according to claim 1,satisfying the following requirements: 1≦X/Y≦8, and 1≦100Y/(X+Y+Z)≦20wherein X is a weight (kg) of the polyamide A1 fed through the feed port(a); Y is a weight (kg) of the organized clay fed through the feed port(a); and Z is a weight (kg) of the polyamide A2 fed through the feedport (b).
 14. A polyamide composite material produced by the process asdefined in claim
 1. 15. A packaging material made of the polyamidecomposite material as defined in claim
 14. 16. A packaging containermade of the polyamide composite material as defined in claim 14.